Merge pull request #1753 from std-freejia/main

[std-freejia] week 02 solutions

Author: SamTheKorean

3sum/std-freejia.java

@@ -0,0 +1,31 @@
+class Solution {
+        public List<List<Integer>> threeSum(int[] nums) {
+
+        List<List<Integer>> answer = new ArrayList<>();
+        Arrays.sort(nums);
+        int len = nums.length;
+
+        for (int i = 0; i < len - 2; i++) {
+            // 인접한 같은 수라면, 지나감 
+            if (i > 0 && nums[i] == nums[i-1]) continue; 
+            
+            int L = i + 1, H = len - 1;
+
+            while(L < H) {
+                if (nums[L] + nums[H] + nums[i] > 0) {
+                    H--;
+                } else if (nums[L] + nums[H] + nums[i] < 0) {
+                    L++;
+                } else {
+                    answer.add(Arrays.asList(nums[i],  nums[L], nums[H]));
+                    // 중복을 제거
+                    while (L < H && nums[L] == nums[L+1]) L++;
+                    while (L < H && nums[H] == nums[H-1]) H--;
+                    L++;
+                    H--;
+                }
+            }
+        }
+        return answer;
+    }
+}

climbing-stairs/std-freejia.java

@@ -0,0 +1,14 @@
+class Solution {
+    public int climbStairs(int n) {
+        int[] dp = new int [n + 1];
+        
+        if (n == 1) return 1;
+        dp[1] = 1;  
+        dp[2] = 2;
+
+        for (int i = 3; i <= n; i++) {
+            dp[i] = dp[i - 1] + dp[i - 2];
+        }
+        return dp[n];
+    }
+}

product-of-array-except-self/std-freejia.java

@@ -0,0 +1,23 @@
+class Solution {
+    public int[] productExceptSelf(int[] nums) {
+    int len = nums.length;
+    int[] res = new int[len];
+    int num = 1;
+
+    for (int i = 0; i < len; i++) {
+        res[i] = num;
+        num *= nums[i];
+    }
+    num = 1;
+    for (int i = len -1; i>=0; i--) {
+        res[i] *= num;
+        num *= nums[i];
+    }
+
+    for (int i = 0; i < len; i++) {
+        System.out.print( res[i] + " ");
+    }
+
+    return res;
+}
+}

valid-anagram/std-freejia.java

@@ -0,0 +1,14 @@
+class Solution {
+    public boolean isAnagram(String s, String t) {
+        if (s.length() != t.length()) return false;
+
+        Map<Character, Integer> mapS = new HashMap<>();
+        Map<Character, Integer> mapT = new HashMap<>();
+
+        for (int i = 0; i < s.length(); i++) {
+            mapS.put(s.charAt(i), mapS.getOrDefault(s.charAt(i), 0) + 1);
+            mapT.put(t.charAt(i), mapT.getOrDefault(t.charAt(i), 0) + 1);
+        }
+        return mapS.equals(mapT);
+    }
+}